2-methylbut-3-yn-2-ol

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

Effects on fertility:

- NOAEL = 130 mg/kg bw (OECD 408)

Link to relevant study records

Reference

Endpoint:

fertility, other

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity in Rodents)

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Route of administration:

oral: gavage

Vehicle:

water

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

90 days

Frequency of treatment:

once daily

Dose / conc.:

45 mg/kg bw/day (nominal)

Dose / conc.:

130 mg/kg bw/day (nominal)

Dose / conc.:

400 mg/kg bw/day (nominal)

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

In all male and all female animals of test group 3 (400 mg/kg bw/d) slight unsteady gait was observed on several days of the study within 2 hours as well as within 2 to 5 hours after administration. The sign was observed first in males on study day 12 and in females on study day 10. Reduced attention was observed in all males and 7/10 females (Nos. 71-76 and 79) of the same test group on several days of the study within 2 hours as well as within 2 to 5 hours after administration. This finding was seen first in males on study day 16 and in females on study day 31. Additionally, in 6/10 male (Nos. 31, 33, 34, 38-40) and 5/10 female (Nos. 72-76) high dose group animals semiclosed eyelids of both eyes was observed within 2 to 5 hours after administration starting on study day 55 in males and on study day 31 in females. Furthermore, in all male and all female animals of test group 2 (130 mg/kg bw/d) slight unsteady gait was observed on several days of the study within 2 hours (except male No. 28 and female No. 64) as well as within 2 to 5 hours after administration. The sign was seen first in in both sexes on study day 37. All animals of test groups 2 and 3 (130 and 400 mg/kg bw/d) recovered from all above mentioned findings overnight. None of the listed findings above had been observed on the next day before treatment. In 1 female (No.58) of test group 1 (45 mg/kg bw/d) slight poor general condition, piloerection and pale skin on entire body was observed within 2 hours as well as within 2 to 5 hours after administration on study day 10. The animal recovered overnight. These unique appearing findings are assessed as incidental and spontaneous in nature and not related to treatment. No clinical findings were observed in male of test groups 1 (45 mg/kg bw/d).

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

no effects observed

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

From beginning of determination (study day 25) until end of administration period water consumption was increased in male animals of test group 3 (400 mg/kg bw/d) with an increase >20% between study days 53-56, 60-63, and 81-84 as well as in males of test group 2 (130 mg/kg bw/d) with an increase >20% between study days 39-42, 46-49, 53-56, and 60-63. In male animals of test group 1 (45 mg/kg bw/d) and in female animals of all test groups water consumption was not increased above 20%.

Ophthalmological findings:

no effects observed

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

At the end of the administration period in males of test groups 2 and 3 (130 and 400 mg/kg bw/d) hematocrit values were significantly decreased. Additionally, in males of both mentioned test groups and of test group 1 (45 mg/kg bw/d) red blood cell (RBC) counts were significantly decreased and relative reticulocyte counts, mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) content were significantly increased. Hematocrit values, MCH and relative reticulocyte counts in males of test groups 1 and 2 were within historical control ranges (males hematocrit 0.410-0.448 L/L, MCH 1.00-1.09 fmol, relative reticulocytes 1.5-1.9 %). RBC counts and MCV in males of test group 1 were also within the historical controls range whereas those of test group 2 were marginally outside these ranges (males RBC 8.31-9.08 Tera/L, MCV 47.8-51.1 fL). MCV is a calculated index using the measured red blood cell parameters hematocrit and RBC counts, the first parameter within, the last one marginally below the historical control range in males of test group 2. Therefore, red blood cell parameter changes in males of test group 1 and 2 (45 and 130 mg/kg bw/d) were regarded as treatment related but not adverse, because none or at maximum one measured parameter (RBC counts in test group 2) were outside historical control ranges (ECETOC Technical Report No 85, 2002). Several red blood cell parameters in males of test group 3 (400 mg/kg bw/d) were clearly outside the historical control ranges and therefore, these changes were regarded as adverse.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

At the end of the administration period in rats of both sexes of test group 3 (400 mg/kg bw/d), alanine aminotransferase (ALT) activities were significantly higher compared to controls. Additionally, in males of test group 1 and 3 (45 and 400 mg/kg bw/d) aspartate aminotransferase (AST) activities were significantly increased. However, the higher AST values in test group 1 were not dose dependently changed and were therefore, regarded as incidental and not treatment-related. The ALT and AST activity means in test group 3 were less than twofold higher compared to those of the study controls. Therefore, these alterations were regarded as treatment-related but not adverse (Hall et al., 2012).

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

No treatment-related changes among urinalysis parameters were observed. However, in rats of both sexes of test group 3 (400 mg/kg bw/d) urine volume was significantly higher compared to controls. This observation per se without any other finding in the urinary tract were regarded as treatment-related but not adverse. In males of test group 3 (400 mg/kg bw/d) significantly higher incidences of oxalate crystals were found in the urine sediment.

Behaviour (functional findings):

effects observed, treatment-related

Description (incidence and severity):

In the functional observation battery performed within 5 hours after treatment, slight impairment of coordination was observed manifested in the unsteady gait, food splay test, and grip strength in test group 3 (400 mg/kg bw/d) and partially in test group 2 (130 mg/kg). Additionally, a reduced motor activity was determined in the test group 3 within 8 hours after treatment. These findings were assessed as clinical pattern of a hypnotic chemical. The test substance is an alcohol with a tertian hydroxyl group with known hypnotic potential (Sehring K 1955). Therefore, these findings were assessed as treatment-related but not adverse.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Treatment-related findings were observed in kidneys and testes of male animals and in ovaries of female animals.
In males of test groups 2 and 3, eosinophilic droplets were noted with treatment-relatedly increased severity in proximal tubules of the kidney. Macroscopic findings of enlargement and discoloration correlated with the histopathological findings in test group 2 and 3. A histopathological correlate for the enlarged kidneys in two test group 1 males and in animal 40 (test group 3, which showed only minimal findings histopathologically) could not be detected. In 5 males of test group 3, minimal retention of spermatids was noted, characterized by two generations of elongated spermatids in tubules of stages X to XII, it was graded minimal, as only a few spermatids of step 19 were present (the mature form, which should have been released in stage VIII). In all females of test group 3, minimal to slight (micro)vacuolation of interstitial glands was observed. No morphological correlates were seen for the increased liver weights in test group 3 males and the decreased pituitary gland weights in test group 3 females.
All other findings occurred either individually or were biologically equally distributed over control and treatment groups. They were considered to be incidental or spontaneous in origin and without any relation to treatment.

Histopathological findings: neoplastic:

no effects observed

Other effects:

not specified

Reproductive function: oestrous cycle:

effects observed, treatment-related

Description (incidence and severity):

Significant test substance-related increase of estrous cycle length (6.5 days) and decrease of the number of cycles (2.3) were obtained in female animals of test group 3 (400 mg/kg bw/d). Female No. 77 of this test group had no complete estrous cycle during the observation period, thus mean cycle length could be determined in 9 of 10 females of test group 3 (400 mg/kg bw/d), only. No test substance-related effects on estrous cycle length and the number of cycles were obtained in female animals of test groups 1 and 2 (45 and 130 mg/kg bw/d).

Reproductive function: sperm measures:

effects observed, treatment-related

Description (incidence and severity):

In males of test groups 1, 2 and 3 (45, 130 and 400 mg/kg bw/d), total sperm counts in the cauda epididymidis were significantly lower compared to controls. However, all values were within the historical control range (TS/gC 381-890 Mio/g) and the change was not dose dependent. Additionally, the percentage of abnormal sperms was statistically increased in males of test group 3 (400 mg/kg bw/d), with the dominating observation of an abnormal hook or a missing head. Abnormal sperm counts were already higher in males of test group 2 (130 mg/kg bw/d), but the change was not statistically significant and the mean was within the historical control range (abnormal sperms 6.0-7.2 %). Therefore, the combination of reduced sperm head counts and increased abnormal sperm counts in males of test group 3 (400 mg/kg bw/d) were regarded as adverse. In males of test group 2 (130 mg/kg bw/d) abnormal sperm head counts were not statistically significantly increased and both mentioned parameters were within historical control ranges. In test group 1 (40 mg/kg bw/d) only total sperm head counts were decreased, but the values were also within the historical control range. Therefore, the mentioned altered sperm parameters in males of test group 1 and 2 were regarded as incidental and not treatment-related. Concerning motility of the sperms and the sperm head counts in the testis no treatment-related effects were observed.

Reproductive performance:

not examined

Dose descriptor:

NOAEL

Effect level:

45 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

gross pathology

histopathology: non-neoplastic

Dose descriptor:

NOAEL

Effect level:

130 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

organ weights and organ / body weight ratios

histopathology: non-neoplastic

Critical effects observed:

yes

Lowest effective dose / conc.:

400 mg/kg bw/day (nominal)

System:

male reproductive system

Organ:

cauda epididymis

testes

Treatment related:

yes

Dose response relationship:

yes

Critical effects observed:

yes

Lowest effective dose / conc.:

400 mg/kg bw/day (nominal)

System:

female reproductive system

Organ:

ovary

Remarks on result:

not measured/tested

Remarks:

The study type of an OECD 408 does not foresee a mating of parental animals to produce an offspring generation. Therefore, no information on the F1 or F2 generation are available.

Reproductive effects observed:

yes

Lowest effective dose / conc.:

400 mg/kg bw/day (nominal)

Treatment related:

yes

Relation to other toxic effects:

reproductive effects occurring together with other toxic effects, but not as a secondary non-specific consequence of other toxic effects

Dose response relationship:

yes

Conclusions:

The administration of 2-methylbut-3-yn-2-ol by gavage to male and female Wistar rats for 3 months caused signs of systemic toxicity manifested on kidney as well as reproductive organs epididymis, testis, and ovary. These findings had been observed largely in the highest dose level tested (400 mg/kg bw/d). However, findings in the kidney of the male animals (macroscopic: enlarged and discolored, histological correlate: increased eosinophilic droplets) were also partially present at mid dose levels (130 mg/kg bw/d). Therefore, under the conditions of the study the no observed adverse effect level (NOAEL) was 45 mg/kg bw/d for male Wistar rats (NOAEL for female Wistar rats = 130 mg/kg bw/d).

Effect on fertility: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

130 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Additional information

2-Methylbut-3-yn-2-ol was administered by gavage to groups of 10 male and 10 female Wistar rats at dose levels of 0 (test group 0, vehicle control), 45 (test group 1), 130 (test group 2) and 400 mg/kg bw/d (test group 3) over a period of 3 months. The application caused signs of systemic toxicity manifested on kidney as well as reproductive organs epididymis, testis, and ovary. The findings on the reproductive organs had been observed in the highest dose level tested (400 mg/kg bw/d) in male as well as in female animals. Therefore, under the conditions of the present study the no observed adverse effect level (NOAEL) for reproductive toxicity was 130 mg/kg bw/d in Wistar rats.

Concerning reproductive toxicity, the spermanalysis showed a combination of reduced sperm head counts in the cauda epidymidis and an increase of abnormal sperm counts in males of test group 3 (400 mg/kg bw/d). This simultaneous occurrence of both effects was regarded as adverse, whereas the not dose-dependent alterations of sperm head counts in test group 1 and 2 (45 and 130 mg/kg bw/d) and the higher abnormal sperm counts in test group 2 were within historical control ranges. Therefore, the changes in these test groups were regarded as incidental and not treatment-related. Regarding the decreased mean relative epididymides weight of test group 3 males (400 mg/kg bw/d), the finding was regarded as treatment-related as it was below historical controls. Furthermore, it might correlate to the histopathologically observed minimal sperm retention in the testis in this group and to decreased spermatocyte numbers observed in clinical pathology. This finding was assessed as adverse.

The alteration of estrous cycle of female animals of test group 3 (400 mg/kg bw/d) with an increase of cycle length and decrease of number of cycles was assessed as treatment-related and adverse. Furthermore, in the ovaries of that test group minimal to slight vacuolation of interstitial glands was observed and assessed as treatment-related and adverse.

In general, any effect of a substance that has the potential to interfere with sexual function and fertility should be considered for classification purposes. This includes, next to others, alterations to the female and male reproductive system as well as reproductive cycle normality. The effects observed after repeated administration of 2-methylbut-3-yn-2-ol give rise to the assumption that there is some evidence of an adverse effect on fertility in males and/or in females although there is no full reprotoxicity study available. Since there is no clear evidence of an adverse effect on fertility, placing the test substance in Category 2 (fertility) seems to be the most appropriate way for classification purposes.

Effects on developmental toxicity

Description of key information

Developmental toxicity:
- NOAEL = 130 mg/kg bw (OECD 414)

Effect on developmental toxicity: via oral route

Dose descriptor:

NOAEL

130 mg/kg bw/day

Additional information

Developmental toxicity was evaluated in a prenatal developmental toxicity study performed in compliance with OECD guideline 414 (BASF, 1997). In this study, 25 female Wistar rats per dose received applications of 45, 130 and 400 mg/kg/day from day 6 through day 15 post coitum.

It was found, that 400 mg/kg bw caused clinical symptoms (apathy, unsteady gait and/or piloerection) throughout the entire treatment period. On the other hand, no effects on the maternal organisms were found when lower doses of 45 and 130 mg/kg bw were administered. Because signs of embryo-/fetotoxicity like increased rate of fetuses showing skeletal retardation was noted only for the high dose group of 400 mg/kg bw, the NOAEL for maternal and embryo-/fetotoxicity was found to be 130 mg/kg bw. Thus developmental toxicity occurred only at the same dose level as maternal toxicity.

Justification for classification or non-classification

Effects on fertility:

An OECD 408 guideline study gives some evidence for an adverse effect on fertility of 2-methylbut-3-yn-2-ol. Therefore, classification seems to be warranted according to the criteria of Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008:

GHS Category 2, fertility (H361f)

Developmental toxicity:

An OECD 414 guideline study gives no hint for any reprotoxic potential of 2-methylbut-3-yn-2-ol. Therefore, classification is not warranted according to the criteria of Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.